Imported WRL not showing in render, initially also hidden in editor
The cause of that is return in 2699th line of code in import_x3d.py which returns the method. Moreover, the color vectors need alpha value to be added.
Fix:

def appearance_CreateMaterial(vrmlname, mat, ancestry, is_vcol):
    bpymat = bpy.data.materials.new(vrmlname)
    diff_color = mat.getFieldAsFloatTuple('diffuseColor', [0.5, 0.5, 0.5, 1], ancestry)

    if(len(diff_color) == 3):
        # .wrl does not have alpha, we need to add 4th element
        diff_color = diff_color+[1]
    bpymat.diffuse_color = diff_color

    bpymat.specular_color = mat.getFieldAsFloatTuple('specularColor', [0.0, 0.0, 0.0], ancestry)

    if False and is_vcol:
        bpymat.use_vertex_color_paint = True
    return bpymat